Structure and method for improving the reliability of surface mounted ceramic duplexers

ABSTRACT

A duplexer assembly is provided and includes a circuit board and a duplexer connected to the circuit board by a joint material, wherein the joint material provides a joint thickness of at least about 10 mils.

BACKGROUND

The present application is directed to duplexer assemblies and, moreparticularly, to structures and method for improving the reliability ofduplexer assemblies.

Ceramic duplexers typically are used in various electronic communicationdevices. In particular, monolithic ceramic duplexers often are used incellular telephone circuits and the like to facilitate the transmissionand receipt of communication signals.

Ceramic duplexers may include a multipole shaped ceramic piece adaptedto connect (e.g., with soft solder or the like) to various metal traceson a printed circuit board. Such ceramic duplexers often are relativelylarge as compared to the size of the printed circuit board. For example,a ceramic duplexer may be about 1.5 inches long, about 0.5 inches wideand about 0.25 inches tall. The connection thickness between theduplexer and the printed circuit board may be in the range of about 1 toabout 5 mils, as commonly obtained using commercial electronic assemblymethods.

Typically, there is a significantly large mismatch between thecoefficients of thermal expansion of the printed circuit board and theceramic duplexer. For example, an epoxy/glass printed circuit board mayhave a coefficient of thermal expansion of about 16 parts per millionper ° C. (“ppm/° C.”) and a ceramic duplexer may have a coefficient ofthermal expansion of about 5 ppm/° C.

Accordingly, due to the significant mismatch between the coefficients ofthermal expansion of the printed circuit board and the ceramic duplexer,as well as the relatively large size of the duplexer, the connectionbetween the duplexer and the printed circuit board is prone to failure.In particular, the joint connecting the duplexer to the traces on theprinted circuit board is prone to cracking when subjected to thermalcycling in the range of about −40° C. to about 85° C.

Attempts to address the connection failures by increasing the surfacearea of the duplexer/circuit board connection (e.g., increasing thesurface area of the solder joint) have failed to remedy the problem. Insome attempts, increasing the surface area of the connection resulted ina transfer of the stress generated by the coefficient of thermalexpansion mismatch to the duplexer, thereby cracking the duplexer.

Accordingly, there is a need for an apparatus and method for connectinga duplexer to a circuit board such that the duplexer assembly is capableof withstanding the stresses typically associated with thermal cycling.

SUMMARY

In one aspect, a duplexer assembly is provided and includes a circuitboard and a duplexer connected to the circuit board by a joint material,wherein the joint material provides a joint thickness of at least about10 mils.

In another aspect, a duplexer assembly is provided and includes aduplexer having at least one connection pad disposed on a surfacethereof, a circuit board having at least one trace disposed on a surfacethereof, the trace being connected to the connection pad by a jointmaterial, and at least one spacer positioned between the duplexer andthe circuit board, the spacer increasing the distance between theconnection pad and the trace.

In another aspect, a method for connecting a duplexer having at leastone connection pad to a circuit board having at least one trace isprovided. The method includes the steps of positioning a spacer betweenthe duplexer and the circuit board to provide an increased space betweenthe connection pad and the trace, positioning a solder material in theincreased space between the connection pad and the trace and increasinga temperature of the solder material such that the solder material meltsand electrically connects the connection pad to the trace.

Other aspects will become apparent from the following description, theaccompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of a first aspect of an improvedduplexer assembly;

FIG. 2 is a front perspective view of the duplexer of the assembly ofFIG. 1 in an inverted position to clearly show the electrical contactsand spacers;

FIG. 3 is a front perspective view of a first alternative aspect of theduplexer of FIG. 2;

FIG. 4 is a front perspective view of a second alternative aspect of theduplexer of FIG. 2;

FIG. 5 is a front perspective view of a third alternative aspect of theduplexer of FIG. 2;

FIG. 6 is a front perspective view of a circuit board according to afirst alternative aspect of the improved duplexer assembly of FIG. 1;and

FIG. 7 is a front elevational view, in section, of a circuit boardaccording to a second alternative aspect of the improved duplexerassembly of FIG. 1.

DETAILED DESCRIPTION

As shown in FIG. 1, a duplexer assembly, generally designated 10, mayinclude a duplexer 12 and a printed circuit board 14. The duplexer 12may be any duplexer known in the art, such as a ceramic duplexer, andmay include a generally planar engaging surface 15 having connectionpads 16 thereon. The printed circuit board 14 may be any circuit boardknown in the art, such as a glass/epoxy circuit board, and may include agenerally planar engaging surface 17 having traces 18 thereon. Thetraces 18 may be substantially aligned with the connection pads 16.

The pads 16 may be connected to the traces 18 by joints 20, which mayhave a stand-off height or joint thickness T separating the duplexer 12from the printed circuit board 14. The thickness T may be generallyuniform across the joints 20 or may vary such that the joints 20 have anaverage overall thickness. The joints 20 may be soft solder or the likeor any other material capable of making a physical and/or electricalconnection between the duplexer 12 and the printed circuit board 14.

It has been discovered that the stress generated by the coefficient ofthermal expansion mismatch between the duplexer 12 and the printedcircuit board 14 may be managed by increasing the thickness T of thejoints 20 between the duplexer 12 and the printed circuit board 14. Inone aspect, the joint thickness T may be about 10 to about 50 mils(i.e., thousandths of an inch). In another aspect, the joint thickness Tmay be about 25 to about 100 mils. In another aspect, the jointthickness T may be increased by about 2 to about 100 times.

Therefore, referring to FIGS. 1 and 2, a first aspect of a duplexer 12may be provided with four spacers 22 extending from the engaging surface15 of the duplexer 12 to increase the joint thickness T between theduplexer 12 and the circuit board 14. Alternatively, one, two, three,five or more spacers 22 may extend from the duplexer 12 in order tomaintain a consistent stand-off height across the duplexer 12.

As shown in FIGS. 1-3 and 6, the spacers 22 may be generallyhemispherical bumps or stand-offs extending from the engaging surface15, wherein the radius of the bumps generally corresponds to the jointthickness T. Those skilled in the art will appreciate that the spacers22 may have various shapes and geometries and may be positioned atvarious locations on the duplexer 12 such that the duplexer 12 is spacedfrom the circuit board 14.

As shown in FIGS. 1 and 2, the spacers 22 may be integrally formed ontothe duplexer 12 during the manufacturing/casting process. Alternatively,as shown in FIG. 3, the spacers 22 may be formed as an add-on component,thereby eliminating the need to retool existing manufacturing equipment.The add-on spacers 22 may be formed from any material capable ofwithstanding solder reflow temperatures and/or thermal cycling, such asunsolderable metals, thermoset or thermoplastic materials or ceramics.The add-on spacers 22 may be connected to the duplexer 12 or formed byany available means, such as brazing, welding, adhesives, press fitting,material forming, molding or the like. For example, the add-on spacers22 may be formed from dots of adhesive applied to the duplexer 12. Theadhesives may include, for example, epoxy, polyimide and silicone, andmay be cured, if necessary.

Alternatively, as shown in FIG. 6, the spacers 22 may be positioned onthe engaging surface 17 of the printed circuit board 14. As discussedabove, the spacers 22 may be integral to the circuit board 14 or may beprovided as an add-on component and may be formed from any of thematerials described above.

In another aspect, as illustrated in FIG. 4, the spacers 22 of FIGS. 1-3and 6 may be replaced with rings or clips 24 capable of engaging theduplexer 12 to space the duplexer 12 from the printed circuit board 14when the duplexer 12 is connected to the printed circuit board 14. Inone aspect, the clips 24 may be removably connected to the duplexer 12and may include a number of bumps or spacers 26 extending from the clip24 to increase the distance T between the duplexer 12 and the circuitboard 14.

Alternatively, the joint thickness T may be increased by increasing thevolume of solder (or other joint material) applied to the joints 20 andcontrolling the surface area to which the solder is allowed to spread.For example, as shown in FIG. 5, the pads 16 may be coated with a largeor thick volume of solder 28. In one aspect, the solder 28 may be pastesolder or solder pre-forms. The solder 28 may be aligned with theappropriate traces 18 on the circuit board 14 and the entire assembly 10may be heated to an appropriate temperature to melt and wet the solder,thereby connecting the pads 16 to the traces 18. A layer of solder mask(not shown) may be applied to the circuit board 14 to control thespreading of the molten solder.

In another aspect, as shown in FIG. 7, a first layer of relatively thicksolder mask 30 may be applied to the circuit board 14 to form a mold 34.The first layer 30 of the mold 34 may be applied such that only thetraces 18 of the circuit board 14 are exposed. An additional layer ofsolder mask 32 may be applied over the first layer 30 to obtain anadditional thickness T and/or alter the shape and/or geometry of theresulting solder mold 34. Those skilled in the art will appreciate thatvarious layers of solder mask 30, 32 may be used, depending upon thedesired thickness T and overall shape of the desired mold 34. The pads16 of the duplexer 12 may then be aligned with the exposed solder 28 andthe assembly 10 may be heated to an appropriate temperature such thatthe solder 28 melts, flows and connects the pads 16 to the traces 18.The resulting duplexer assembly 10 may have a joint thickness T, whichmay be substantially equal to or greater than the total solder maskthickness (i.e., the thickness of layers 30 and 32) due to the firstlayer 30 restricting the wettable area on the printed circuit board 14.

Although the improved duplexer assembly is shown and described withrespect to certain aspects, modifications may occur to those skilled inthe art upon reading the specification. The improved duplexer assemblyincludes all such modifications and is limited only by the scope of theclaims.

1. A duplexer assembly comprising: a circuit board; a duplexer connectedto said circuit board by a joint material, wherein said joint materialprovides a joint thickness of at least about 10 mils; and at least onespacer positioned between said duplexer and said circuit board, whereinsaid spacer is connected to and extends from said duplexer.
 2. Theassembly of claim 1 wherein said joint thickness is an average overallthickness of said joint material.
 3. The assembly of claim 1 whereinsaid joint thickness is about 10 mils to about 50 mils.
 4. The assemblyof claim 1 wherein said joint thickness is about 25 mils to about 100mils.
 5. The assembly of claim 1 wherein said joint material is softsolders.
 6. The assembly of claim 1 wherein said circuit board has acoefficient of thermal expansion that substantially differs from acoefficient of thermal expansion of said duplexer.
 7. The assembly ofclaim 1 wherein said duplexer includes a ceramic material and saidcircuit board includes at least one of glass and an epoxy.
 8. Theassembly of claim 1 wherein said spacer is a generally hemisphericalstand-off.
 9. The assembly of claim 1 wherein said spacer is connectedto and extends from said circuit board.
 10. The assembly of claim 1wherein said spacer is a deposit of adhesive applied to at least one ofa surface of said duplexer and a surface of said circuit board.
 11. Theassembly of claim 1 wherein said spacer is a clip connected to saidduplexer to increase the distance between said duplexer and said circuitboard.
 12. The assembly of claim 1 wherein said joint material isapplied using a mold formed from a solder mask.
 13. The assembly ofclaim 1 wherein at least one of said circuit board and said duplexerincludes a relatively thick layer of pre-applied solder, said solderbeing adapted to form said joint material.
 14. A duplexer assemblycomprising: a duplexer having at least one connection pad disposed on asurface thereof; a circuit board having at least one trace disposed on asurface thereof, said trace being connected to said connection pad by ajoint material; and at least one spacer positioned between said duplexerand said circuit board, said spacer increasing the distance between saidconnection pad and said trace, wherein said spacer is connected to andextends from said duplexer.
 15. The assembly of claim 14 wherein saidjoint material is a soft solder.
 16. The assembly of claim 14 whereinsaid distance between said connection pad and said trace is at leastabout 10 mils.
 17. The assembly of claim 14 wherein said circuit boardhas a coefficient of thermal expansion that substantially differs from acoefficient of thermal expansion of said duplexer.
 18. A method forconnecting a duplexer having at least one connection pad to a circuitboard having at least one trace, said method comprising the steps of:positioning a spacer between said duplexer and said circuit board toprovide an increased space between said connection pad and said trace,wherein said spacer is connected to and extends from said duplexer;positioning a solder material in said increased space between saidconnection pad and said trace; and increasing a temperature of saidsolder material such that said solder material melts and electricallyconnects said connection pad to said trace.